The present invention is directed to an optical switch for switching light between an input waveguide and one or more output waveguides.
Optical switches are essential components in an optical network for determining and controlling the path along which a light signal propagates. Typically, an optical signal (the terms xe2x80x9clight signalxe2x80x9d and optical signalxe2x80x9d are used interchangeably herein and are intended to be broadly construed and to refer to visible, infrared, ultraviolet light, and the like), is guided by a waveguide along an optical path, typically defined by the waveguide core. It may become necessary or desirable to redirect the optical signal so that it propagates along a different optical path, i.e., through a different waveguide core. Transmission of an optical signal from one waveguide to another may require that the optical signal propagate through a medium which may have an index of refraction different than the index of refraction of the waveguides (which typically have approximately the same refractive index). It is known that the transmission characteristics of an optical signal may be caused to change if that signal passes through materials (mediums) having different indices of refraction. For example, an unintended phase shift may be introduced into an optical signal passing from a material having a first index of refraction to a material having a second index of refraction due to the difference in velocity of the signal as it propagates through the respective materials and due, at least in part, to the materials"" respective refractive indices. Additionally, a reflected signal may be produced due to the mismatch of polarization fields at the interface between the two mediums. As used herein, the term xe2x80x9cmediumxe2x80x9d is intended to be broadly construed and to include a vacuum.
This reflection of the optical signal is undesirable because it reduces the transmitted power by the amount of the reflected signal, and so causes a loss in the transmitted signal. In addition, the reflected signal may travel back in the direction of the optical source, which is also known as optical return loss. Optical return loss is highly undesirable, since it can destabilize the optical signal source.
If two materials (or mediums) have approximately the same index of refraction, there is no significant change in the transmission characteristics of an optical signal as it passes from one material to the other. One solution to the mismatch of refractive indices involves the use of an index matching fluid. A typical use in an optical switch is to fill a trench between at least two waveguides with a material having an index of refraction approximately equal to that of the waveguides. Thus, the optical signal does not experience any significant change in the index of refraction as it passes through the trench from one waveguide to another.
An example of that solution may be found in international patent application number WO 00/25160. That application describes a switch that uses a collimation matching fluid in the chamber between the light paths (i.e., between waveguides) to maintain the switch""s optical performance. The use of an index matching fluid introduces a new set of considerations, including the possibility of leakage and a possible decrease in switch response time due to the drag on movement of the switching element in a fluid.
In addition, the optical signal will experience insertion loss as it passes across a trench and between waveguides. A still further concern is optical return loss caused by the discontinuity at the waveguide input/output facets and the trench. In general, as an optical signal passes through the trench, propagating along a propagation direction, it will encounter an input facet of a waveguide which, due to physical characteristics of that facet (e.g., reflectivity, verticality, waveguide material, etc.) may cause a reflection of part (in terms of optical power) of the optical signal to be directed back across the trench (i.e., an a direction opposite of the propagation direction). This is clearly undesirable.
Size is also an ever-present concern in the design, fabrication, and construction of optical components (i.e., devices, circuits, and systems). It is clearly desirable to provide smaller optical components so that optical devices, circuits, and systems may be fabricated more densely, consume less power, and operate more efficiently.
The present invention is directed to an optical switch having an input waveguide and two output waveguides separated by and disposed around a trench. The input waveguide and the first output waveguide have respective optical paths defined by their respective cores; those optical paths (and cores) generally being aligned or coaxial with each other. The trench has a medium provided therein that has a refractive index different from that of the waveguides. Back reflection is therefore avoided, since the input waveguide, the first output waveguide, and the second output waveguide are separated by a distance insufficient to affect the transmission characteristics of an optical signal propagating from the input waveguide to either the first or second output waveguide, even though the optical signal experiences different refractive indices as it propagates from the input waveguide to the first or second output waveguides. Thus, even though an optical signal passing from the input waveguide to either output waveguide must completely traverse the trench, the distance over which the optical signal must travel between the waveguides is small enough so as to not affect the optical transmission characteristics of that signal.
The input waveguide and the second output waveguide are arranged generally on the same side of the trench such that an optical signal passing from the input waveguide to the second output waveguide does not completely traverse the trench. Once again, even though the optical signal experiences different indices of refraction, it propagates over a distance too small to adversely affect the optical transmission characteristics of that signal.
Both 1xc3x972 and 2xc3x972 optical switches can be constructed in accordance with this invention.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the disclosure herein. The scope of the invention will be indicated in the claims.